It is by now well known to use organomolybdenum compounds in lubricating oil compositions to decrease friction between moving parts. In oils used to lubricate internal combustion engines lowering of friction between moving parts increases fuel efficiency. As well as oils for internal combustion engines, organomolybdenum compounds may also be used in functional fluids such as manual and automatic transmission fluids, wet brakes fluids, hydraulic fluids and other comparable fluids.
The organomolybdenum compounds used in lubricating compositions are molybdenum containing alkyl and dialkyl dithiocarbamates and their oxyo and/or sulfurized analogs. Examples of such organomolybdenum compounds are disclosed in the following patent publications, all of which are incorporated herein by reference.
Japanese Patent Laid-Open Application No. 56202/1973 teaches a compound having the general formula [R.sub.2 N--CS.sub.2 ].sub.2 --Mo.sub.2 S.sub.4 wherein R is an alkyl group, which compound is useful as an additive for lubricants. But that compound has a corrosive action on copper-containing materials, so the use of that compound has been limited.
Japanese Patent Laid-Open No. 62-81396, for example, proposes a molybdenum-containing lubricant additive with an excellent oxidation preventive function, wear proofing function, friction mitigating function and metal corrosion inhibiting function, and further is highly soluble in a base oil such as mineral oil. Japanese Patent Laid-Open No. 48-56202 proposes an extreme pressure lubricant containing MoDTC blended thereto.
Further, Japanese Patent Laid-Open No. 5-279686 proposes a lubricating oil composition for an internal combustion engine prepared by blending (a) sulfurized oxymolybdenum dithiocarbamate and/or sulfurized oxymolybdenum organophosphorodithioate, (b) fatty acid ester and/or organoamide compound, (c) at least one compound selected from the group consisting of calcium sulfonate, magnesium sulfonate, calcium phenate and magnesium phenate, (d) at least one compound selected from the group consisting of benzylamine and boron derivatives of benzylamine, and (e) zinc dithiophosphate and/or zinc dithiocarbamate, in a base oil for a lubricating oil.
Japanese Patent Laid-Open No. 5-230485 proposes a lubricating oil composition for an engine oil containing, as essential components in a base oil using a mineral oil and/or a synthetic lubricating oil, (a) an alkaline earth metal salt of alkyl-salicylic acid, (b) a bis-type alkenylsuccinic acid imide having a polybutenyl group and/or its derivative, and (c) sulfurized oxymolybdenum organophosphorodithioate and/or molybdenum dithiocarbamate.
Japanese Patent Laid-Open No. 5-186787 proposes a lubricating oil composition prepared by blending (a) sulfurized oxymolybdenum dithiocarbamate and/or sulfurized oxymolybdenum organophosphorodithioate and (b) zinc dithiophosphate and/or zinc dithiocarbamate into a mineral oil, and further proposes a lubricating oil composition prepared by adding (c) an organic amide compound to the above.
Japanese Patent Laid-Open No. 5-163497 proposes an engine oil composition comprising (A) a base oil consisting of a mineral oil and/or a synthetic oil, (B) a boron compound derivative of alkenylsuccinic acid amide, (C) an alkaline earth metal salt of salicylic acid and (D) molybdenum dithiophosphate and/or molybdenum dithiocarbamate, as the principal components.
A molybdenum dihydrocarbyldithiocarbamate compound useful as an additive for lubricants is disclosed in U.S. Pat. No. 4,098,705 to Sakurai et al.
Novel sulfur and phosphorus containing molybdenum compositions which are useful for improving fuel economy for internal combustion engines are disclosed in U.S. Pat. No. 4,289,635 to Schroeck.
U.S. patent to NTN Corporation of Japan recites a grease composition for constant velocity joints comprising a urea grease including a lubricating oil and a urea base thickener and containing (A) 1-5% by weight of molybdenum sulfide dialkyldithiocarbamate, (B) 0.2-1% by weight of molybdenum disulfide, (C) 0.5-3% by weight of an extreme pressure additive of zinc dithiophosphate and (D) 0.5-5% by weight of an oiliness agent composed of at least one of vegetable oils and fats as an essential component, provided that a weight ratio of the component (B) to the component (A) is 0.04-0.5.
The instant invention does not contain a urea base thickener or molybdenum disulfide.
U.S. Pat. No. 5,627,146 to Asaki Denka Kogyo describes alkyl group asymmetric molybdenum dithiocarbamate having increased oil solubility.
International patent application published under publication number WO 96/06904 to the Tonen Corporation describes a composition having good lubricity and comprising a major amount of a lubricant base oil, a basestock of lubricating viscosity, to which a minor amount of additives has been added. The additives comprise specific amounts of oxymolybdenum dithiocarbamate sulfide having specific alkyl groups, zinc dialkyldithiophosphate having specific alkyl groups, one or more specific sulfur containing compounds, an ashless dispersant and a boron containing additive which may be the ashless dispersant. In further aspects of the invention a metal detergent is used. Conveniently, the dispersant and boron are added as a borated succinimide.
The invention of WO 96/06904 is a lubricant composition comprising a major amount of a lubricant base oil having added thereto a minor amount of additives comprising (A) oxymolybdenum dithiocarbamate sulfide having alkyl groups with 8 to 18 carbon atoms, (B) zinc dialkyldithiophosphate having primary alkyl groups with 1 to 18 carbon atoms, (C) one or more additional peroxide decomposing sulfur compounds, (D) an ashless dispersant, and (E) a boron containing additive in an amount sufficient to provide at from 0.005 to 0.06% by weight boron to the finished lubricant wherein to the total weight of the composition, the molybdenum content from oxymolybdenum dithiocarbamate sulfide is at 200 to 2,000 ppm (ratio by weight); the phosphorus content from zinc dialkyldithiophosphate is at 0.02 to 0.15% by weight; and the sulfur content from the additional peroxide decomposing sulfur compound is at 0.02 to 0.30% by weight. Conveniently, the additional peroxide decomposing sulfur compound is selected from the group consisting of zinc dialkyldithiocarbamate, copper dialkyldithiocarbamate or nickel dialkyldithiocarbamate wherein the dialkyldithiocabamate has alkyl groups with 2 to 18 carbon atoms, bis(dialkyldithiocarbanoyl)disulfide having an alkyl group with 2 to 18 carbon atoms, disulfide having an alkyl group with 2 to 18 carbon atoms, disulfide having an allyl group, an alkylallyl group or an allylalkyl group with 6 to 18 carbon atoms, olefin sulfide, fish oil sulfide, whale oil sulfide and mixtures of any of the foregoing.
WO 96/06904 describes in detail the use of additional sulfur compounds in the compositions described.
The additional sulfur compound required by WO 96/06904 is selected from any of the sulfur compounds that efficiently decompose peroxides. Without intending to be bound by any theory, the extended fuel economy performance of the present invention may be attributable to suppressed consumption of the oxymolybdenum dithiocarbamate sulfide and the zinc dialkyldithiophosphate because the sulfur compounds efficiently decompose peroxides.
As the dialkyldithiocarbamate salt to be blended in the lubricant composition of the invention, use is made of a compound represented by the general formula (3) ##STR1##
wherein M represents zinc, copper or nickel; R.sup.9, R.sup.10, R.sup.11 and R.sup.12 may be the same or different, each representing an alkyl group with 2 to 18 carbon atoms. Metal salts of dialkyldithiocarbamic acid are well known and readily available. Processes for their synthesis are described in U.S. Pat. Nos. 4,623,473 and 4,740,322.
The alkyl group of 2-18 carbon atoms represented by R.sup.9, R.sup.10, R.sup.11 and R.sup.12 in the general formula (3) may be linear or branched, including for example, an ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group and octadecyl group.
As the bis(dialkyldithiocarbamoyl)disulfide to be blended in the lubricant composition of the present invention, use may be made of a compound represented by the general formula (4): ##STR2##
wherein R.sup.13, R.sup.14, R.sup.15 and R.sup.16 may be the same or different, each representing an alkyl group with 2 to 18 carbon atoms. The alkyl group of 2-8 carbon atoms represented by R.sup.13, R.sup.14, R.sup.15 and R.sup.16 in the general formula (4) may be linear or branched, including for example an ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group and octadecyl group.
As the disulfide to be blended in the lubricant composition of the invention, use is made of a compound represented by the general formula (5): EQU R.sup.17 --S--S--R.sup.18 (5)
wherein R.sup.17 and R.sup.18 may be the same or different, each representing an alkyl group with 2 to 18 carbon atoms or an allyl group, an alkylallyl group or an allylalkyl group, with 6 to 18 carbon atoms. The alkyl group of 2-8 carbon atoms represented by R.sup.17 and R.sup.18 in the general formula (5) may be linear or branched, including for example an ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group and octadecyl group; the allyl group, the alkylallyl group or the allylalkyl group, having 6 to 18 carbon atoms and being represented by R.sup.17 and R.sup.18, includes for example a phenyl group, benzyl group, phenetyl group, methylbenzyl group, diphenylmethyl group and the like.
Olefin sulfide, fish oil sulfide and whale oil sulfide, to be blended with the lubricant composition of the invention, should be olefin sulfide (polysulfide) being produced by sulfide processing of polymers such as isobutylene and having a sulfur content of 25 to 40% by weight, fish oil sulfide and whale oil sulfide produced by processing individually fish oil and whale oil in the same manner.
European Patent Application EP 07251 30A2 to the Tonen Corporation describes a lubricating oil composition containing a majority of an oil of lubricating viscosity, a molybdenum dithiocarbamate, an organozinc compound, and a phenol based antioxidant.
Thus, it is known in the art to use organomolybdenum compounds to reduce frictional properties of lubricant oils and to use sulfur compounds as sulfur donors, as well as phenolic antioxidants, to suppress oxidative degradation of the organomolybdenum compounds.